15:30 〜 15:45
[PEM09-22] Impact evaluation of Dellinger phenomena during solar flares using GAIA model
キーワード：デリンジャー現象、太陽フレア、電離圏
The sudden increase in X-ray to extreme ultraviolet (EUV) emissions from solar flares can cause ionization in the ionosphere and cause rapid variations in electron density. The communication failure caused by the absorption of short-wave due to fluctuations in electron density in the ionospheric D region (60-90 km) is called the Dellinger phenomenon (Dellinger 1937). The occurrence of the Dellinger phenomenon can be known from the value of the minimum reflection frequency (fmin) observed by the vertical incident ionosonde. It is known that the variation of the fmin value depends on the flare class (X-ray peak flux of flare) and the solar zenith angle (e.g., Tao et al., 2020). However, there are many cases in which the fmin value is not proportional to the flare class. In order to reveal the relationship between solar flare spectra and their ionospheric variations that affect the Dellinger phenomenon, it is necessary to consider flare emission wavelengths other than X-rays, which affect the electron density of the entire ionosphere.
We first investigated the relationship between X-ray (GOES/XRS) and EUV (GOES/EUVS-E and SDO/EVE) emissions observed during flare events, and fmin values obtained from ionosondes which are provided by the National Institute of Information and Communications Technology (NICT) in Wakkanai, Kokubunji, Yamagawa and Okinawa. In this study, we statistically analyzed 38 solar flare events of >M3 class observed during daytime in Japan (9:00-18:00 JST) between May 2010 and May 2014. Comparing these X-ray and EUV emissions with fmin values, it was found that Lyman-alpha emission was not correlated with fmin. On the other hand, X-ray (1-8 Å) and EUV (11-14 nm) emissions were correlated with fmin, with correlation coefficients of 0.74 and 0.76, respectively.
Next, using the Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy (GAIA), a physical model of the Earth's atmosphere, and the Appleton-Hartree equation to calculate the ionospheric effects of solar flare spectrum and compared them with the observed Dellinger phenomenon (fmin). Detailed event analysis of the X1.7-class flare on May 13, 2013 shows that the main source of ion density fluctuations is X-ray in the D region and 11-14 nm EUV emission in the E and F regions. The absorption of the short-wave was found to be ~90-100 % in the D region and ~10 % in the E region.
Finally, we tried to estimate the magnitude of the Dellinger phenomenon. The estimation accuracy using only the GAIA calculation results was 0.81 for the correlation coefficient between the predicted and the observed fmin values, while the blackout capture rate was 31 %. On the other hand, when the GAIA calculation results and the solar zenith angle-corrected X-ray flux Fχ were used as the variable for ion density in the D region, the correlation coefficient between the predicted and observed fmin values was 0.85 and the blackout capture rate was 62 %. Therefore, we found that the prediction accuracy of the Dellinger phenomenon was improved by using Fχ as a variable for ion density variations in the lower ionosphere.
We first investigated the relationship between X-ray (GOES/XRS) and EUV (GOES/EUVS-E and SDO/EVE) emissions observed during flare events, and fmin values obtained from ionosondes which are provided by the National Institute of Information and Communications Technology (NICT) in Wakkanai, Kokubunji, Yamagawa and Okinawa. In this study, we statistically analyzed 38 solar flare events of >M3 class observed during daytime in Japan (9:00-18:00 JST) between May 2010 and May 2014. Comparing these X-ray and EUV emissions with fmin values, it was found that Lyman-alpha emission was not correlated with fmin. On the other hand, X-ray (1-8 Å) and EUV (11-14 nm) emissions were correlated with fmin, with correlation coefficients of 0.74 and 0.76, respectively.
Next, using the Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy (GAIA), a physical model of the Earth's atmosphere, and the Appleton-Hartree equation to calculate the ionospheric effects of solar flare spectrum and compared them with the observed Dellinger phenomenon (fmin). Detailed event analysis of the X1.7-class flare on May 13, 2013 shows that the main source of ion density fluctuations is X-ray in the D region and 11-14 nm EUV emission in the E and F regions. The absorption of the short-wave was found to be ~90-100 % in the D region and ~10 % in the E region.
Finally, we tried to estimate the magnitude of the Dellinger phenomenon. The estimation accuracy using only the GAIA calculation results was 0.81 for the correlation coefficient between the predicted and the observed fmin values, while the blackout capture rate was 31 %. On the other hand, when the GAIA calculation results and the solar zenith angle-corrected X-ray flux Fχ were used as the variable for ion density in the D region, the correlation coefficient between the predicted and observed fmin values was 0.85 and the blackout capture rate was 62 %. Therefore, we found that the prediction accuracy of the Dellinger phenomenon was improved by using Fχ as a variable for ion density variations in the lower ionosphere.